Polycarbonate resins are representative thermoplastic materials having a thermal deformation temperature of about 135° C. or more. Polycarbonate resins exhibit excellent mechanical properties in terms of impact resistance, self extinguishability, dimensional stability, thermal resistance, and transparency. Thus, polycarbonate resins are widely used in the manufacture of exterior materials for electric/electronic products, office equipment, automobile components, and as optical films, and the like.
However, despite good transparency and mechanical properties, conventional polycarbonate resins have limitations as exterior materials. When a plastic material is used as an exterior material, the plastic material is generally painted to provide a pleasant appearance. In this case, paints are diluted in various organic solvents, followed by deposition and drying of the diluted paints on a surface of a resin article. In this process, the organic solvents used as diluents infiltrate into polycarbonate, thereby causing deterioration in transparency and mechanical strength. In addition, when polycarbonate resins are prepared by melt polymerization at high temperatures, fine gels can be produced by Fries rearrangement, and can create pin holes on the surfaces of thin articles such as films and the like, which are produced using the polycarbonate resins.
Thus, polycarbonate resins require chemical resistance in order to be used in articles exposed to various organic solvents and must prevent formation of fine gels at high temperature in order to be used in various applications such as optical films and the like.
As a method for improving chemical resistance, a polycarbonate resin can be blended with a resin having chemical resistance to suppress infiltration of an organic solvent. Although this method can slightly improve chemical resistance, there is a problem of deterioration in impact resistance. In this case, although an impact modifier can be used to improve the deteriorated impact resistance due to blending, there is a problem of significant deterioration in transparency of the resin. To improve chemical resistance, a method for preparing a copolymerized polycarbonate by adding a material having chemical resistance upon polymerization of the polycarbonate is disclosed in Japanese Patent Publication No. H5-339390A, U.S. Pat. No. 5,401,826, and the like. One example of a material having chemical resistance may include 4,4′-biphenol (BP), which may be copolymerized with bisphenol A to improve chemical resistance. However, even in the case of using a material having chemical resistance such as 4,4′-biphenol (BP), it is difficult to prevent or reduce formation of the fine gel due to high reaction temperature.
Therefore, there is a need for a polycarbonate resin that can prevent deterioration in external appearance due to fine gels and can exhibit excellent chemical resistance without deterioration of inherent properties, such as thermal resistance, transparency, and the like.